This invention is directed to devices and equipment for collecting bulk solids, for example, process dust coming from a dust generator, such as a sanding machine, wherein the dust is entrained in a flow of air from the source machine, and is separated out at a dust collection station where the dust falls into a dust collection container, e.g., drum or barrel. The invention is more specifically directed to a compact and efficient system for sensing whether the dust collection drum is filled or nearly filled with accumulated production dust, and alerting the operator so the drum can be properly emptied.
In any process equipment that involves filling drums, containers, silos, boxes, etc., there is a need for an indicator system to signal when capacity of the container (or a desired level within the container) has been reached. Without an indicator system operators are forced to monitor the levels manually, and can risk overfilling. In some cases, overfilling can cause major system failures, filter clogging, and costly downtime.
Many types of machines for processing a workpiece, require means to dispense with the grindings, chips, and particulate matter that is generated during operation. For example, in the case of wood working machines, such as sanders, joiners, and the like, wood that is removed from a workpiece has to be collected and removed from the work area because the dust creates a breathing hazard for the workman as well as a fire hazard. More specifically, in the case of portable equipment, such as floor sanders and edgers, it is conventional to draw off the dust that is generated by the machines and then send the air that is carrying the dust into a filter bag arrangement, or to draw off the dust through a flexible hose or conduit. In such case, the conduit or hose extends from a dust outlet duct of the machine to a collection station. A stream of air is pumped through the conduit, with the entrained process dust. An example of a dust collection system of this general type is shown in U.S. Pat. No. 6,833,016, which is incorporated herein by reference. The bulk solids collection drum may have a drum liner so that the collected dust descends into the liner, i.e., a plastic bag, for easy removal and disposal.
At the dust collection station, the air flow and entrained process dust are drawn through a cyclone separator situated above the dust storage drum or barrel. The process dust falls into a the film bag or liner in the barrel, and the air then proceeds to a pumping and filtering arrangement, where the dust-free air is discharged back into the ambient environment.
It is important that the dust collection drum, and/or any drum liner, be emptied out when it becomes filled or nearly filled. A fill detector of one type or another may be used so sense that the level of accumulated dust is nearing the top of the drum or barrel. One method of doing this has been to used a motorized rotary paddle wheel that can rotate freely until the upper level of the accumulated dust reaches the paddle wheel and slows or stops it. These devices have tended to be cumbersome and unreliable, and can cease to function for any of a number of mechanical reasons, including breakage of a paddle blade or vane. Rotating paddle type sensor switches rely on a rotating paddle that protrudes into the container. When the material level rises to cover the paddle, the movement of the paddle is impeded, and the switch closes. These devices are costly, have moving parts, and add complexity to the system. The devices also require a deep penetration into the container, which poses a problem for sensing level near the lid of the dust collection drum. When protruding through a drum lid, these paddle type sensors make the removal of the drum lid difficult, since the paddle is lodged down deep in the drum contents. With a limited clearance available, it can be difficult or impossible to use these sensors mounted in a drum lid. Paddle-type sensors are also fixed-depth, so changing to a different depth measurement requires mechanically changing the paddle or the shaft of the device.
Accordingly, there has been a need for a dust drum level detector that senses accumulated dust level without having to physically touch or move the dust, and which does not have moving parts that can break or fail. It is also desirable to provide a strong visible alert when the dust drum has become full, where the high sound level in the shop would make an audible alert difficult to hear.